The present invention relates to a method for producing improved biological pesticides. Biological pesticides produced via the method have improved resistance to environmental degradation, especially that caused by exposure to ultra-violet (UV) light and/or heat. The method works particularly well for Bacillus thuringiensis toxin but can also be used to protect other toxins such as those produced by other Bacillus strains and by UV sensitive viruses and/or fungi.
The UV sensitivity of such biological pesticides is well known. By use of the process described herein, the UV sensitivity of the active toxins in such biopesticides can be greatly reduced.
A number of microencapsulation systems have been proposed for providing protection of agriculturally active substances.
One method suggested in U.S. Pat. No. 3,839,561 utilizes diisophorone derivatives to protect active cyclopropane carboxylic acid compounds from ultra-violet induced degradation. Similarly, U.S. Pat. No. 4,094,969 describes the use of a sulfonated copolymer of catechin and leucocyanidin as a UV stabilizer. In both cases, however, the formulations suggested do not maintain the sunscreen and active ingredient in close enough contact to be effective.
In U.S. Pat. No. 3,242,051, a method for coating materials by phase separation is described. Gelatin and various carboylated polymers such as gum acacia and ethyl cellulose are used to form the coating. The use of a similar ethylcellulose/gelatin system is described by Ignoffo and Batzer in "Microencapsulation and Ultraviolet Protectants to Increase Sunlight Stability of an Insect Virus", J. Econ. Entomology, Vol. 64, pp. 850-853 (1966), and the use of a chlorophyll green/gelatin system is described in U.S. Pat. No. 2,090,109. In these cases, however, the materials have less than desirable environmental stability. Another disadvantage of these polymers is that they are not always capable of keeping the sunscreening agent within the capsule wall.
Encapsulation of actives by interfacial polycondensation is described in U.S. Pat. Nos. 4,280,833 and 4,417,916. The actives thus formed have a skin or thin wall of polyurea which improves release characteristics and environmental stability. In the process, lignin sulfonate is used as an emulsifier.
The use of lignin in controlled release of actives is also known in the prior art. The preparation of controlled release composites of lignin and biologically active materials is described in U.S. Pat. No. 3,929,453 (Re. 29,238). The composites described are obtained by coprecipitation-inclusion from an aqueous alkaline lignin solution, or by the elimination of a common solvent from a lignin-biologically active organic agent mixture. Preparation of reversibly swellable lignin gels is described in U.S. Pat. Nos. 4,184,866 and 4,244,729. The described gels are formed by crosslinking lignin with epichlorohydrin and are able to sustain the release of water-soluble and water-insoluble pesticides. The use of other crosslinking agents such as formaldehyde and glutaric dialdehyde is described in a related U.S. Pat. No. 4,244,728. The use of said gels for UV protection, however, is not disclosed in any of these patents.
The use of sunscreen agents in combination with encapsulation is described in U.S. Pat. No. 4,844,896. Suggested sunscreen agents include methyl orange, malachite green, methyl green and other colored dyes, and suggested encapsulating agents include Eudragit L, Eudragit S, polyacrylic acid and other polyacrylates. It is claimed that such systems keep the sunscreen agent within the capsule. Incorporation of the sunscreen into the capsule wall is not disclosed, however, and the problem of sunscreen catalyzed degradation is not addressed.
U.S. Pat. Nos. 4,844,896 and No. 4,948,586 describe methods for encapsulating insecticidal pathogens together with sunscreen agents in polyacrylate encapsulating agents. The sunscreens used include dyes such as methyl green and methyl orange (U.S. Pat. No. 4,844,896) and organic chemicals such as bezophenone and p-aminobenzoic acid (U.S. Pat. No. 4,948,586). Both of the methods described, however, are relatively complex and the sunscreens used are quite costly. A similarly described process using lignin as a sunscreen agent is described in International Application No. PCT/US92/03727. While the use of lignin reduces the cost of the sunscreen, the process involved is still complex and relatively costly.
In "Protection of Bacillus Thuringiensis from Inactivation by Sunlight", Can. Ent. 115, pp. 1215-1227 (1983), Morris examined the effects of addition of a number of varied sunscreening agents on the UV stability of commercially available Bacillus thuringiensis formulations. In "Photoprotection of Bacillus thuringiensis kurstaki from Ultraviolet Irradiation", J. Invert, Path., 57, pp. 343-351 (1991), Cohen, et al conducted similar studies with cationic chromophores as the selected sunscreens. Margulies, et al in Arch. Insect Biochem. Physiol., 22, pp. 467-486 (1993) reported the effects of cationic dyes and/or mixtures of cationic dyes and clays on the UV stability of biological and chemical pesticides. While increased protection was reported in all three studies, treatment costs were quite high.
The objective of this invention, on the other hand, is to react ultra-violet sunscreens, and more specifically sulfonated lignins, sulfonated lignites, naphthalene sulfonates, and other related compounds, directly with a protein toxin to form a stable complex. Chemical bonds keep the sunscreen agents from diffusing out of the complex where they are ineffective. A further objective of incorporation of the sunscreen directly with the toxin is to minimize sunscreen catalyzed degradation of sensitive actives.
Still another objective of the invention is to minimize the number of ingredients needed in the procedure, thereby simplifying the overall process and minimizing production costs.
Other objectives and advantages of the invention will become evident on reading the following detailed descriptions.